LED-based light-emitting devices are becoming more and more popular. One of the reasons for this popularity is the long lifetime of LEDs (light-emitting diodes). However, the lifetime of currently available LED-based light-emitting devices may sometimes be limited not by the LEDs themselves, but by other parts of the light-emitting device, such as the electrical connection between LED-module and circuit board.
In currently available LED-based light-emitting devices, a LED-module is often soldered to a regular printed circuit board (PCB), which may often be made of, for example, FR-4. Due to mismatch in the thermal expansion behavior of the LED-module and the PCB, temperature cycling may eventually result in defects in the solder connection between the LED-module and the PCB, which may lead to premature failure of the LED-based light-emitting device.
WO02/12788A1 discloses a LED assembly including an electrically and thermally conductive heat dissipater sandwiched under an electrically insulating layer with circuit traces disposed over the insulating layer to prevent electrical conduction between the traces and the heat dissipater. A plurality of LEDs have electrical leads extending laterally from opposite extremities of each LED to overlie the traces for electrical contact with the traces for powering the LEDs. An independent and generally U-shaped holding device, as viewed in cross section, defines a base overlying the LED and a pair of legs depending therefrom and transversely to the electrical leads between the LED and the heat dissipater. The base defines a hole and the LED protrudes through the hole to emit light. The insulating layer includes a void surrounding each LED and the legs of each associated holding device and each holding device includes a tensioning portion for applying a force urging the LED through the void and into thermal engagement with the heat dissipater and the electrical leads thereof into engagement with the traces. To solve this problem and to prolong the life of LED-based light-emitting devices, it has been proposed to replace the regular PCB with a circuit board that has a coefficient of thermal expansion that more closely matches that of the LED-module. Such a circuit board may, for example, be ceramic-based. Although solving the lifetime problem, the replacement of the regular PCB by a ceramic-based circuit board results in a higher cost. Furthermore, ceramic-based circuit boards are brittle, which may limit the form factor of the light-emitting device.